The object of this project is the development of a parathyroid hormone (PTH) bioassay sensitive to physiological concentrations of hormone. Hormone effects on 3', 5'-cyclic AMP accumulation and adenyl cyclase activity are measured in cells and cell membranes from rat calvaria, chick epiphyses and rat osteosarcoma. Membrane purification and cell cloning are used to increase the sensitivity and specificity of the above target tissues to hormone. Bone from osteopetrotic rats (incisor absent) and mice (microphtalmic) is studied to examine the role of adenyl cyclase stimulation in the mechanism of action of PTH.